Simfit is a free software OpenSource Windows/Linux package for simulation,
curve fitting, statistics, and plotting, using
a library of models or user-defined equations.
It can be used in:

biology (nonlinear growth curves);

ecology (Bray-Curtis dendrograms);

psychology (factor analysis);

physiology (membrane transport);

pharmacology (dose response curves);

pharmacy (pharmacokinetics);

immunology (ligand binding);

biochemistry (calibration);

biophysics (enzyme kinetics);

epidemiology (survival analysis);

medical statistics (meta analysis);

chemistry (chemical kinetics);

physics (dynamical systems); and

mathematics (numerical analysis).

Simfit has forty programs, each dedicated to an aspect of
simulation, plotting, or data analysis, with a reference manual containing
mathematical and statistical details.
Tutorials and worked examples explain how to analyze the
default data sets supplied for every procedure.

Clipboard data and spreadsheet export files can be analyzed, and macros to interface
with Microsoft Office are provided.

Simdem is a package demonstrating how to use the Simfit
GUI and graphics library to write Windows programs with menus, tables, and graphs.